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1

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Nanostructuring of tips for scanning probe microscopy by ion sputtering: Control of the apex ratio and the tip radius (2001)

Hoffrogge, P. ; Kopf, H. ; Reichelt, R.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 90 (2001), S. 5322-5327

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Ion etching under well-defined conditions represents a very powerful tool to fabricate tips in a controlled and reproducible manner for Scanning Probe Microscopy which possess clean, relatively smooth, and oxide-free surfaces. The possibilities and limitations of ion etching are demonstrated thoroughly for tungsten, which is of particular interest for scanning tunneling microscopy. Iterative computer simulations and experimental studies are provided. The simulation of the etching process at the atomic level is based on the Monte Carlo program (Transport of Ions in Matter), which provides reliable values for the key input parameters such as the sputtering yield Y(θ,Eion) and the mean ion range in the material for ion energies between 1 and 6 keV. The simulation program starts with a large tip radius as a crude form and asymptotically approaches a "final form" of a very sharp tip in the course of ion etching. Our experimental results with argon ions in the energy range up to 6 keV and crude electrochemically etched polycrystalline tungsten wire agreed very reasonably with the simulated results. For example, the minimum tip radius obtained experimentally amounts to approximately 5 nm. This value corresponds closely to the ion range, which obviously sets a limit to the smallest achievable tip radius by the effect of transmission sputtering. By variation of the angle between the ion beam and the macroscopic tip, the tip angle can be controlled in the range between 12° and 35°. © 2001 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1406548

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2

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Patterns in the use of space by benthic communities on two coral reefs of the Great Barrier Reef (1986)

Reichelt, R. E. ; Loya, Y. ; Bradbury, R. H.

Springer

Coral reefs 5 (1986), S. 73-79

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ISSN: 1432-0975

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract A rapid benthic line-transect survey method for use by non-specialist observers is described. At both Davies Reef (mid-continental shelf) and Myrmidon Reef (outer-continental shelf) in the central Great Barrier Reef a set of 6 sites of varying depths on the reef flat, crest and slope were sampled using this method. At least 10 contiguous 10 m transects were made at each site. Benthic organisms were recorded as life forms with categories based on both high level taxa and morphologies, and including scleractinian corals, alcyonarians, sponges, algae and others. Percentage cover data for 19 benthic categories are presented for all sites. Coral cover on both reefs is high on the crest and slope but low on the reef flat. At all sites the cover of soft corals and sponges is much less than cover of hard corals and algae. Abundances of soft corals and sponges increase with depth. Analysis of gaps between hard corals show that many colonies grow close to each other (〈1 cm)even when total coral cover is low.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00270355

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Patterns in the structural typology of benthic communities on two coral reefs of the central Great Barrier Reef (1986)

Bradbury, R. H. ; Loya, Y. ; Reichelt, R. E. ; [et al.]

Springer

Coral reefs 4 (1986), S. 161-167

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ISSN: 1432-0975

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract The morphological life-forms, that is to say, physiognomic-structural attributes, of two coral reef communities were used in a numerical analysis to determine the power of these attributes in recovering the underlying community structure. We used 17 attributes from the benthic communities at 6 reef slope sites on each of a midshelf and off-shore reef of the central Great Barrier Reef. These reefs had been previously well studied by traditional species-level means for several major taxonomic groups such as corals, fish and soft corals. Our multivariate analyses were able to recover broad patterns of between-reef affinity and discrete within-reef zonation patterns similar to those found in earlier studies, and in broad accord with the prevailing model of reef community structure, but with far greater efficacy. But perhaps more importantly, by placing all the benthos within the same context for the first time, our analyses were able to recover new patterns of community structure independent of the ones described earlier. This suggests that single-model explantations for the complex phenomena of coral reefs are likely to be inadequate.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00427937

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4

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Patterns in the distribution of the crinoid community at Davies Reef on the central Great Barrier Reef (1987)

Bradbury, R. H. ; Reichelt, R. E. ; Meyer, D. L. ; [et al.]

Springer

Coral reefs 5 (1987), S. 189-196

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ISSN: 1432-0975

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract The crinoid community of Davies Reef, a midshelf reef in the central Great Barrier Reef, was systematically sampled in all major crinoid habitats. A total of 294 individuals of 27 species-level taxa was found in 25 sites across the reef. Of these 27 taxa, 20 were confidently assigned to known species. The 25 sitesx27 taxa matrix was subjected to an array of pattern extraction and diagnostic techniques — numerical classification, ordination and minimum spanning trees — to elucidate the structure of the community. These analyses revealed a consistent structure characterized by a species-rich ensemble around the periphery of the reef which was attenuated towards the inside of the reef. This structure contrasts strongly with the patterns seen in other major reef communities, such as hard and soft corals, fish or sponges. In these communities, different parts of the reef are characterized by distinctive sets of species, a depthbased zonation of the communities is evident, and the fore-reef slope typically supports a different ensemble from the back-reef slope. We conclude that the crinoid community offers a significant opportunity to observe the coral reef ecosystem from a different perspective.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00300962

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5

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Patterns of predictability in coral reef community structure (1987)

Green, D. G. ; Bradbury, R. H. ; Reichelt, R. E.

Springer

Coral reefs 6 (1987), S. 27-34

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ISSN: 1432-0975

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract The question of whether population numbers are predictable in coral reef communities is confronted directly by trying to predict abundances of benthic taxa both within and between two reefs on the central Great Barrier Reef. Using models derived via the Group Method of Data Handling (GMDH), taxon abundances were found to be more predictable at Davies Reef than at Myrmidon Reef and a significant number of taxa showed consistent predictability patterns in all tests. For most taxa, the predictability of benthic abundances increased steadily with increasing spatial scale. Water depth figured prominently in almost all of the models obtained, emphasizing its importance as a physical determinant of local taxon abundances.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00302209

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6

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An assessment of the geological evidence for previous Acanthaster outbreaks (1986)

Moran, P. J. ; Reichelt, R. E. ; Bradbury, R. H.

Springer

Coral reefs 4 (1986), S. 235-238

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ISSN: 1432-0975

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract Much debate has surrounded the notion that outbreaks of the crown-of-thorns starfish (Acanthaster planci) have occurred in the geological past and hence are natural phenomena. As this debate has recently been renewed, we have reassessed statistically data presented by Frankel (1977, 1978) as evidence for the occurrence of past outbreaks. This was done using Frankel's data as well as those from extensive starfish surveys conducted prior to the commencement of his research. Our analysis of these data indicates that the occurrence of A. planci remains in recent sediments is independent of whether or not the reef from which the sample was collected had experienced a recent outbreak. Based on this premise, it is not possible to infer from Frankel's data the occurrence of past outbreaks from similar material in much older sediments. Thus while the data presented by Frankel (1977, 1978) may show that A. planci has existed within the Great Barrier Reef for at least several thousand years it does not demonstrate that outbreaks of this starfish have occurred in the geological past.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00298082

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7

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Distribution of recent outbreaks of the crown-of-thorns starfish (Acanthaster planci) along the Great Barrier Reef: 1985–1986 (1988)

Moran, P. J. ; Bradbury, R. H. ; Reichelt, R. E.

Springer

Coral reefs 7 (1988), S. 125-137

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ISSN: 1432-0975

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract A large survey program was conducted during 1985/1986 to determine the extent of activity of the crown-of-thorns starfish, Acanthaster planci, and its broad effects on the coral communities of the Great Barrier Reef (GBR). The perimeters of 228 reefs (about 9% of reefs in the GBR system) were surveyed within 1 year using rapid survey, manta tow techniques. These reefs encompassed the broad latitudinal and longitudinal gradients within the GBR. Approximately 27% (62 reefs) of the reefs surveyed had recently experienced (18%), or were experiencing (9%), an outbreak of the crown-of-thorns starfish. These outbreaks were mainly confined to reefs in the central third of the GBR (between Lizard Island and Townsville) and had affected, to varying degrees, approximately 65% of the reefs surveyed within this region. A greater proportion of mid-shelf reefs had experienced outbreaks than outer-shelf reefs, although this difference was not statistically significant. Of the small number of inner-shelf reefs surveyed, none had been recently affected by an outbreak. Large active outbreaks of starfish were reported on many of the reefs located off Townsville while much smaller outbreaks were found on several reefs at the southern end of the GBR, in the Swain Reef complex. Almost 86% of reefs currently experiencing an outbreak had moderate to high coral mortality over at least a third of their perimeters. Only 10% of reefs with active outbreaks had high coral mortality over most of their windward and leeward margins. A similar proportion of reefs had low to moderate coral mortality over less than a third of their perimeters.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00300972

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