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  • Articles: DFG German National Licenses  (6)
  • 1995-1999  (3)
  • 1990-1994  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Direct-current method for differentiating contact and bulk low frequency resistance fluctuations (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2802-2807 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Electronic conductance fluctuations, which have often been used as a detailed probe of electronic transport properties, are known to originate from the metal/material contact region as well as from the material itself. In this article, a measurement technique of conductance fluctuations is presented that differentiates between material bulk fluctuations and contact fluctuations. While it was developed for noise studies on high resistance materials (〉100 k Ω) where other methods of eliminating or identifying contact noise may not be possible, the method is applicable for all sample resistance ranges. The measurement circuit is a variation of the well-known four-probe technique used to eliminate the influence of the direct-current contact resistance from the sample resistance measurement. A battery supplies the dc current but does not act as a constant current source, while two low-noise preamplifiers measure the current and voltage fluctuations simultaneously. By comparing the real time fluctuations in the current and voltage across pair-wise variations of the four probes, and in particular, determining whether the current fluctuations are symmetric or antisymmetric with the voltage fluctuations, the spatial region of the sample responsible for the noise can be directly identified. This technique does not eliminate contact noise but is a sensitive means of distinguishing contact from bulk fluctuations. Examples of systems for which this method will be useful include high impedance semiconductors, where an insulating or Schottky barrier at the metal/semiconductor interface may generate noise from a separate process that is comparable to or greater in magnitude than the bulk noise. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149798
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of bending stress on taper and growth of stems of youngEucalyptus regnans trees (1996)
    Springer
    Trees 10 (1996), S. 239-246 
    Details
    ISSN: 1432-2285
    Keywords: Bending stress ; Stem shape ; Radial growth rate ; Eucalyptus regnans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A glasshouse experiment investigated the effect of bending stress on stem radial and height growth and stem taper ofEucalyptus regnans seedlings. Eighteen-week-old, potted seedlings were bent continuously for 8 weeks with a static bending stress. The bending treatment was then removed and the seedlings grown for another 12 weeks. Other seedlings were stayed vertically throughout the experiment whilst control seedlings were neither bent nor stayed. Seedlings were rotated every 2 days to prevent reaction wood developing asymmetrically in the stems of bent trees. Bent trees had higher radial growth rates, developed more tapered stems and had higher safety factors (the ratio of stem radius to the minimum radius required to prevent the tree toppling over) than unbent seedlings. They produced a band of tension wood in their stems and ceased height growth whilst bent. When bending ceased, they resumed normal radial and height growth. Unbent trees developed more cylindrical stems. There were no differences in growth behaviour between stayed and control trees. Bent and unbent trees all developed a butt swell, the taper of which was not affected by treatment. It was concluded that bending stress has substantial effects on both the size and taper of tree stems. However, the development of butt swell is independent of the bending stress applied. The results were considered in relation to biomechanical theories of tree stem development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02185675
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of bending stress on taper and growth of stems of young Eucalyptus regnans trees (1996)
    Springer
    Trees 10 (1996), S. 239-246 
    Details
    ISSN: 0931-1890
    Keywords: Key words Bending stress ; Stem shape ; Radial growth rate ; Eucalyptus regnans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  A glasshouse experiment investigated the effect of bending stress on stem radial and height growth and stem taper of Eucalyptus regnans seedlings. Eighteen-week-old, potted seedlings were bent continuously for 8 weeks with a static bending stress. The bending treatment was then removed and the seedlings grown for another 12 weeks. Other seedlings were stayed vertically throughout the experiment whilst control seedlings were neither bent nor stayed. Seedlings were rotated every 2 days to prevent reaction wood developing asymmetrically in the stems of bent trees. Bent trees had higher radial growth rates, developed more tapered stems and had higher safety factors (the ratio of stem radius to the minimum radius required to prevent the tree toppling over) than unbent seedlings. They produced a band of tension wood in their stems and ceased height growth whilst bent. When bending ceased, they resumed normal radial and height growth. Unbent trees developed more cylindrical stems. There were no differences in growth behaviour between stayed and control trees. Bent and unbent trees all developed a butt swell, the taper of which was not affected by treatment. It was concluded that bending stress has substantial effects on both the size and taper of tree stems. However, the development of butt swell is independent of the bending stress applied. The results were considered in relation to biomechanical theories of tree stem development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02185675
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Predicting tree diameter and height from above-ground biomass for four eucalypt species (1991)
    Springer
    Trees 5 (1991), S. 30-35 
    Details
    ISSN: 1432-2285
    Keywords: Allometry ; Eucalyptus ; Height prediction ; Diameter prediction ; Mechanistic models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Previous work has suggested that tree stems are structured dimensionally to resist the forces to which they are subjected by the weight of the crown and the action of wind, snow and other loads on the crown. This proposition has been used to develop allometric relationships relating diameter at breast height or height of individual trees growing in even-aged monoculture to their above-ground fresh biomass. These models have practical application as estimators of tree diameters or heights from tree biomass as extensions of mechanistically based models of forest tree growth which predict tree biomasses. The present work applied these models to Eucalyptus regnans F. Muell, E. delegatensis R. Baker, E. nitens (Deane: Maiden) Maiden and E. grandis Hill ex Maiden trees, growing in plantation or regrowth stands, aged between 1.5 and 20 years, at eight geographically diverse sites extending from temperate to sub-tropical regions of Australia. While the models held for the various species at the various sites, their parameter values differed significantly between sites and/or species. This suggested there may be some inadequacy in the models. However, the differences were small and it was found reasonable to fit single models across all species and sites for practical use in estimating diameter or height. The errors about predicted values of height and diameter from these models were quantified. The models were also found to estimate diameter or height with little loss of precision when dry biomass was used in place of fresh biomass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00225332
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Breakage of hollow tree stems (1994)
    Springer
    Trees 9 (1994), S. 47-50 
    Details
    ISSN: 1432-2285
    Keywords: Stem defect ; Tree breakage ; Wood engineering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Stems of trees hollowed by agents such as fungal decay, fire or termites have reduced strength and increased likelihood of breakage. This may pose a serious hazard when hollow trees are growing near public places. Previous theoretical studies and field studies of hollow trees, of both hardwood and softwood species, in Europe and America have suggested rules to quantify the risk of breakage of hollow trees. These rules are confirmed and expanded here, using data collected from hollow trees of several species of the hardwood genus Eucalyptus in Australia. It is concluded that where the ratio of the minimum wall thickness of a stem hollow to the total radius of the hollow exceeds 0.3–0.35 and at least one-half of the girth of the tree stem is intact, it is extremely unlikely that the stem of the hollow tree will break. These rules appear to apply for a wide range of tree species throughout the world.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197869
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of post-planting applications of granulated atrazine and fertiliser on the early growth of Eucalyptus nitens (1994)
    Springer
    New forests 8 (1994), S. 323-333 
    Details
    ISSN: 1573-5095
    Keywords: atrazine ; establishment ; eucalypt plantations ; nitrogen-fertiliser ; phosphorusfertiliser ; triazine herbicides ; weed control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A factorial experiment was established in a plantation of Eucalyptus nitens in southern Tasmania on a site which had formerly carried native eucalypt forest. Before planting, the site had been cleared of weeds with foliar translocated and pre-emergence herbicides. The first factor of the experiment examined the effects on tree growth of no post-planting weed control, control by hand or with three levels of application of granulated atrazine, 0.9, 1.8 and 8 kg ha−1. The second factor examined the effects of no fertiliser application or the application of nitrogen as urea at 200 kg ha−1 N plus triple superphosphate at 120 kg ha−1 P. Tree growth responses to treatments were examined at 11, 16, 23 and 29 months of age. Fertiliser application increased tree height and diameter growth. Application of atrazine generally reduced height and diameter growth, but this was statistically significant only at the highest rate of application. Growth reduction occurred even though atrazine reduced post-planting weed cover on the site and hence potential competition with the tree crop for site resources. Hand weeding reduced the weed crop on the site even more than atrazine, but this did not increase growth of the tree crop. Given satisfactory establishment practices which include the use of herbicides pre-planting, it was concluded that post-planting weed regeneration was not sufficiently vigorous to warrant post-planting weed control on these sites. The use of atrazine for post-planting weed control could even be deleterious to eucalypts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00036732
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    Paper (German National Licenses)
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