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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3557-3559 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the temporal variation of the visible photoluminescence from rapid thermally oxidized porous silicon prepared from n+ substrates. In contrast to the red (slow band) emission, which is observable immediately after high-temperature oxidation, the blue (fast band) emission is shown to become prevalent only after samples are stored in ambient air. The intensity of the blue emission increases with progressive aging, the magnitude of the increase being dependent on the temperature at which the material is oxidized. Thermal treatment of aged rapid thermally oxidized material can reduce and even quench the blue photoluminescence. Quenching is reversible in that the photoluminescence re-appears after further aging at room temperature. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2825-2832 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The suitability of ion-beam-analysis techniques in quantifying the composition of mesoporous silicon nanostructures has been critically examined using films of moderate porosity (55%) prepared on n+ substrates. The effects of room-temperature aging of as-etched and thermally oxidized porous silicon, the oxidation conditions chosen to render the material luminescent, have been carefully monitored, as have the effects of both ion-beam irradiation and storage of samples in vacuo. It is shown that the concentrations of the three major impurities oxygen, carbon, and hydrogen can be appreciably altered during analyses, thereby limiting the reliability of the techniques, as conventionally applied to porous silicon. The use of appropriate capping layers, which should alleviate the problem, is recommended.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2764-2773 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Trends in the efficiency and small signal modulation behavior of porous silicon light emitting diodes (LEDs) are reported for devices formed by the anodization of bulk silicon p–n junctions. As the average size of the silicon skeleton is decreased, the external electroluminescence (EL) efficiency increases from 0.001% to 0.18% and there is a corresponding blue shift in the EL peak from 776 to 633 nm. An associated tenfold increase is observed in the photoluminescence efficiency while the diode resistance, at 2 V, increases from 3×103 to 1×106 Ω. Under small signal pulsed operation, the voltage dependence of the rising edge of the EL is well described by a carrier mobility of 3×10−4 cm2 s−1 V−1 which is independent of the average size of the luminescent regions of the silicon nanostructure. The falling edge of the EL transient is dominated by radiative recombination of quantum confined excitons. The modulation speed is found to be limited by a combination of carrier mobility in the silicon wires and radiative recombination processes. Evidence of charge trapping and discharge is found in an EL overshoot phenomenon. The major application of this type of porous silicon LED, with modulation speeds below 1 MHz, appears to be for displays integrated with circuitry rather than for optical interconnection.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 107-109 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Blue photoluminescence is observed, with nanosecond decay time, from rapid thermally oxidized porous silicon as a result of accelerated aging in plastic containers. Photoluminescence measurements, combined with chemical analyses of the "aged" porous silicon, indicate that the emission is a consequence of the incorporation of trace organic (hydrocarbon) contamination from the plastic containers as they outgas at a mildly elevated temperature (80 °C) and, albeit at a reduced rate, at room temperature. Such carbonaceous contaminants can subsequently be removed by high-temperature annealing, a process which also quenches the blue photoluminescence. Consequently, it is important to take into consideration the storage medium used when making comparative luminescent and compositional studies of porous silicon and, perhaps, porous materials in general. © 1997 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Melbourne, Australia : Blackwell Science Asia Pty. Ltd.
    Austral ecology 26 (2001), S. 0 
    ISSN: 1442-9993
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The floral visitors of silky oak, Grevillea robusta A. Cunn. ex R.Br., their foraging behaviour and their effects on fruit-set were studied at Malava, western Kenya. Grevillea robusta is a popular tree for farm plantings in the eastern and central African highlands. Yield of seed has been disappointingly low in some areas and a lack of appropriate pollinators has been suggested as a possible cause. Investigations involved the monitoring of visitors on active inflorescences, assessment of the rewards available to potential pollinators, and exclusion experiments to establish the effects of various visitors on fruit-set. The flowers are visited mainly by birds and insects. The likely pollinators of G. robusta are sunbirds (Nectarinia amethystina, N. cyanolaema, N. olivacea, N. superba and N. venusta) and white-eyes (Zosterops kikuyuensis and Z. senegalensis). Very little aggressive behaviour between birds was recorded. No nocturnal pollinators were observed. Nectar was the major floral reward for pollinators, but is likely depleted by ants and honey bees, the foraging behaviour of which confirmed them to be nectar-robbers. These insects hardly ever touched stigmas during their visits. Eighty-nine per cent of bird visits were in the morning (07.00–10.00 hours) when nectar volume was highest. Inflorescences bagged to exclude birds set no fruits, and unmanipulated flowers and flowers bagged with self-pollen set no fruits, indicating a self-incompatibility mechanism. Control cross-pollinated flowers displayed greatly increased fruit-set (25.1%) compared with natural open-pollination (0.9%). All these findings confirm the importance of cross-pollen transfer to flowers and the necessity of pollinators for fruit-set. Effective seed production requires activity of pollinators for self-pollen removal and cross-pollen deposition. Seed production stands for G. robusta should be established where flowering is prolific and bird pollinators are abundant.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 89 (1994), S. 713-718 
    ISSN: 1432-2242
    Keywords: Oil palm germplasm ; RAPD Genetic diversity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The genetic variation among different accessions of oil-palm germplasm collected from Africa was estimated using random primers and the polymerase chain reaction. The present study revealed high levels of genetic variation in these accessions. Electrophoresis of the amplification products indicated that nine out of 20 primers were able to generate polymorphic products ranging in length from 0.2 kb to 2.3 kb. No individual palm or population-specific products were observed. Greatest diversity was seen in Zaire population 5 and the least in Zaire population 2.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Agroforestry systems 18 (1992), S. 197-212 
    ISSN: 1572-9680
    Keywords: agroforestry ; breeding ; genetic improvement ; multipurpose trees ; non-industrial trees
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Improvement strategies applicable to non-industrial trees with a clear focus on: end-use target group of beneficiaries, amount of planting material required, the biology of the species and the amount and structure of variation are discussed. Whichever strategy is used it is paramount that material is properly evaluated in trials and that diverse and productive germplasm is released. Cognizance of farmer's needs and criteria should be taken given that they are generally risk averse and try to stabilise production rather than solely maximise production. The consequences of release of planting stock need to be considered in relation to whether improvement will be recurrent or a single event. The establishment of breeding seedling orchards that perform the combined functions of resource population, breeding population, progeny test and seed production area would appear to offer distinct advantages. Decision strategies for improvement of non-industrial trees are discussed in relation to the features outlined.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Agroforestry systems 38 (1997), S. 165-176 
    ISSN: 1572-9680
    Keywords: fruit trees ; non-timber forest products ; tree improvement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract New initiatives in agroforestry are seeking to integrate into tropical farming systems indigenous trees whose products have traditionally been gathered from natural forests. This is being done in order to provide marketable products from farms that will generate cash for resource-poor rural and peri-urban households. This poverty-alleviating agroforestry strategy is at the same time linked to one in which perennial, biologically diverse and complex mature-stage agroecosystems are developed as sustainable alternatives to slash-and-burn agriculture. One important component of this approach is the domestication of the local tree species that have commercial potential in local, regional or even international markets. Because of the number of potential candidate species for domestication, one crucial first step is the identification of priority species and the formulation of a domestication strategy that is appropriate to the use, marketability and genetic potential of each species. For most of these hitherto wild species little or no formal research has been carried out to assess their food value, potential for genetic improvement or reproductive biology. To date their marketability can only be assessed by their position in the local rural and urban marketplaces, since few have attracted international commercial interest. To meet the objective of poverty alleviation, however, it is crucial that market expansion and creation are possible, hence for example it is important to determine which marketable traits are amenable to genetic improvement. While some traits that are relatively easy to identify do benefit the farmer, there are undoubtedly others that are important to the food, pharmaceutical or other industries that require more sophisticated evaluation. This paper presents the current thinking and strategies of ICRAF in this new area of work and draws on examples from our program.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Plant cell, tissue and organ culture 14 (1988), S. 129-136 
    ISSN: 1573-5044
    Keywords: Pinus ; nutrient ; micropropagation ; liquid culture media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Shoot apices of a clone of Pinus caribaea Morelet were cultured and multiplied in vitro by supporting them with their basal cut ends immersed in a liquid nutrient medium. The initial heights of explants and their initial numbers of leaves were positively correlated with the numbers of buds and shoots produced by the explants after a bud induction phase and after a shoot elongation phase. The final numbers of buds and shoots were positively correlated with reductions in the quantities of phosphorus detected in the media and negatively correlated with the numbers of brown leaves produced on the explants. In a comparison between the growth of shoot explants on liquid and solid media, shoots incubated on the liquid medium showed significantly greater increases in length in a four-week period than those cultured on solid medium. This technique, using liquid media, provides a system in which both the nutrient utilization and the growth rates of isolated pine tissues can be readily assessed. Furthermore, the multiplication rate of the tissue can be predicted following the observation of correlated characters early in the micropropagation cycle.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 48 (1976), S. 487-487 
    ISSN: 0009-286X
    Keywords: Extraktion ; Stoffaustausch ; Längsvermischung ; Pulsieren ; Füllkörperkolonne ; Stoffaustauschfläche ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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