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  • 1
    Electronic Resource
    Electronic Resource
    Sapphire resonator for the measurement of surface impedance of high-temperature superconducting thin films (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 2121-2126 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A technique using cavity perturbation of a cooled sapphire disk resonator has been developed to measure the surface impedance Zs=Rs+iXs of high-temperature superconducting thin films. The resonator is excited in the TE011 mode at 14.4 GHz and induces a-b plane screening currents in the sample. The resonator and its enclosure are maintained at 4.2 K while the sample is heated independently on a movable sapphire rod. The thermal isolation of the sample and resonator leaves the measurement virtually free of systematic error and permits the use of a superconducting niobium shield. The combination of low dielectric loss sapphire and a superconducting enclosure results in typical unloaded quality factors (Q) of several million. The ability to move the sample makes the sensitivity variable, allowing surface resistance values from 5 μΩ to several Ω to be measured. Background loss can also be accurately determined at the time of experiment by withdrawing the sample from the influence of the resonator. In addition, sensitive measurements of the penetration depth can be made by spring-loading the film onto quartz spheres glued to the resonator surface; this technique is shown to be free of systematic error up to a temperature of 60 K. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148106
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  • 2
    Electronic Resource
    Electronic Resource
    Split-ring resonators for measuring microwave surface resistance of oxide superconductors (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 1819-1823 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A cavity perturbation technique using split-ring resonators has been developed for measuring the surface resistance of metals in the frequency range 0.3–5.0 GHz. The system is designed particularly for measurements of films and crystals of high-Tc oxide superconductors. The small size of split-ring resonators in this frequency range makes them useful for measuring crystals with areas as small as 0.1 mm2. The measurement geometry is favorable for the study of films because the sample screens its substrate from the microwave fields. The resonator temperature can be kept fixed at 4.2 or 1.2 K for sample temperatures as high as 120 K and this thermal isolation from the sample allows the use of a superconducting split-ring resonator. An unloaded Q of 1.2×106 has been achieved with a superconducting resonator at 1.78 GHz and this makes it sensitive enough to detect surface resistances of the order of a few μΩ. This resonator has been used to measure the surface resistance (25 μΩ/(D'Alembertian)) of a 1-mm2 crystal of Bi2Sr2CaCu2O8.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142427
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  • 3
    Electronic Resource
    Electronic Resource
    Transmission properties of an oak canopy in relation to photoperception (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 8 (1985), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The spectra of incoming daylight and shadelight in a mature oak woodland were measured at intervals during the canopy cycle, and mean transmittance spectra were derived. Transmittance was spectrally neutral at ca. 0.55 during the light phase but, following leaf emergence, transmittance of PAR (400–700 nm) fell to ca. 0.1. Simultaneously, the red : far-red transmittance ratio fell to circa 0.6. Both showed little change during the summer and autumn until senescence, indicating that the optical properties of the canopy were surprisingly stable. There was no evidence that cloud cover influenced mean canopy transmittance, although transient sunflecks introduced great variability which, in combination with sampling bias, might explain previous contradictory reports. The red : far-red fluence rate ratio in the woodland showed a temporary increase in late summer, a result of a small increase in the red : far-red ratio of incoming daylight during this period. Reflectance and transmittance spectra and pigment content of sun and shade leaves were measured. Leaf transmittance spectra showed changes correlated with those of the canopy, and were related to changes in pigment content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1985.tb01686.x
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  • 4
    Electronic Resource
    Electronic Resource
    Some observations on the spectral distribution characteristics of short-wave radiation within Pinus radiata D. Don canopies (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 8 (1985), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Measurements of the photosynthetic photon flux density (400–700 nm) and of the spectral distribution of photon flux density across the 370–800 nm waveband, were made under both clear and overcast sky conditions above and at various positions within two Pinus radiata canopies of different stocking but similar leaf area indices. The spectra obtained for the daylight conditions (i.e. above forest canopy) were generally similar to those published previously. The spectra for shadelight within the forest canopy showed no blue peak which was characteristic of previously reported measurements which were restricted to the diffuse radiation component. There was almost neutral absorption within the 400–700 nm waveband, and typical lower attenuation in the 700–800 nm waveband. The blue: red ratio was largely unchanged by either canopy type or sky conditions and varied between 0.57 and 0.81. The red: far-red ratio in shadelight was between 0.22 and 0.41 under clear sky and between 0.68 and 0.95 under overcast sky conditions. Values for daylight were between 1.16–1.22. Calculated phytochrome photoequilibrium values in shadelight were approximately 0.35 under clear sky and 0.46 under overcast sky conditions. In each case there appeared to be no differences between the two canopies with respect to these minimum values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1365-3040.ep11604610
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  • 5
    Electronic Resource
    Electronic Resource
    Growth and development of Pinus radiata D. Don: the effect of light quality (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 6 (1983), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Plants of Pinus radiata of two physiological ages, juvenile (seedlings and micropropagated plantlets) and adult (rooted cuttings from mature trees), were grown under lighting fromthree combinations of metal halide (MH) and tungsten halogen (TH) lamps for up to 10 months in controlled environment rooms. The three lamp combinations, MH alone, 50: 50 MH: TH and 25:75 MH: TH by wattage, produced red: farred ratios of 4.59, 1.51, and 1.15, respectively. Photosynthetic photon flux density was 700 μmol m−2 s−1. An increase in proportion of TH lamps markedly increased shoot elongation and internode length, decreased numbers of fascicles per unit stem length and increased the proportion of stem weight in both juvenile and adult material. In addition, in adult material, it increased the number of fascicle initials and expanded fascicles per growth flush, reduced the duration of the ‘rest’ phase between growth flushes, accelerated the rate of elongation growth during each flush, and increased apical dominance. Tracheid length, but not diameter or wall thickness, was significantly affected by light quality and found to be associated with longer internodes. Any treatment effects on needle weight or length, stem diameter or root weight were non-significant or very small. Different clones from either the juvenile micro-propagated material or the mature rooted cuttings each showed similar patterns of response, although they often differed in the degree of response to light quality. The main response could be related solely to the red: far-red ratio and the calculated phytochrome photoequilibrium. This is the first report of phytochrome-controlled photomorphogenesis in older specimens of a woody perennial. Recommendations for artificial light sources for growing P. radiata and some ecological implications of the results are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1365-3040.ep11589321
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  • 6
    Electronic Resource
    Electronic Resource
    The influence of simulated shadelight and daylight on growth, development and photosynthesis of Pinus radiata, Agathis australis and Dacrydium cupressinum (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 12 (1989), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Juvenile seedlings, micropropagated plantlets, and adult rooted cuttings of Pinus radiata, together with seedlings of Agathis australis and Dacrydium cupressinum, were grown under either high (670/μmol m−2 s−1) or low (200 μmol m−2 s−1) photosynthetic photon flux density (PPFD) and, at low PPFD, under three red:far-red (R/FR) conditions, approximately simulating canopy shadelight, daylight and one intermediate value. In all types of P. radiata, a shade-intolerant species, stem height and diameter, stem and needle dry weight, and apical dominance were markedly increased by a reduction in R:FR ratio while fascicle density was decreased. In contrast, these increases were considerably less for the shade-tolerant D. cupressinum and moderately tolerant A. australis. With the exception of the P. radiata seedlings, height growth was greatest in all species under high compared to low PPFD for daylight R:FR ratio conditions. Total shoot (or plant) dry weight was increased approximately two-fold in all species and types by the higher PPFD. Shoot extension rates were negatively correlated with calculated phytochrome photoequilibrium with P. radiata, the most shade-intolerant species, having the highest change in rate per unit change in photoequilibrium (i.e. very responsive), and D. cupressinum, the most shade tolerant species evaluated, having the smallest change (i.e. largely unresponsive). Within the spectral quality treatments at low PPFD, it is suggested that higher rates of dry matter accumulation under the low R:FR ratio were the result of reduced mutual shading of adjacent leaves as a consequence of photomorphogenically-controlled internode lengths rather than of enhanced photosynthesis per se. The significance of the results is discussed in relation to planting stock management in nurseries, the management of forest canopies for understorey seedling growth, and to the construction of representative growth simulation models. Consequences for controlled environment lighting are also considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1989.tb01951.x
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  • 7
    Electronic Resource
    Electronic Resource
    The relationship between phytochrome-photoequilibrium and Development in light grown Chenopodium album L. (1978)
    Springer
    Planta 142 (1978), S. 187-193 
    Details
    ISSN: 1432-2048
    Keywords: Chenopodium ; Far-red ; Photoequilibrium ; Phytochrome ; Stem extension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chenopodium album seedlings were grown in light environments in which supplementary far-red light was mixed with white fluorescent light during various parts of the photoperiod. Both the logarithmic rate constant of stem extension and the leaf dry weight: stem dry weight ratio were linearly related to estimated phytochrome photoequilibrium (ϕ) in each treatment regime. These data are taken to be indicative of a functional link between phytochrome and development in the green plant. A layer of chlorophyllous tissue only affected the linearity between calculated ϕ and the logarithmic stem extension rate at high chlorophyll concentrations, whilst even low concentrations-equivalent to the levels found in stem tissue-caused a significant shift in measured ϕ. End-of-day supplementary far-red (FR) light induced between 0–35 per cent of the response elicited by all-day supplementary FR, whilst daytime supplementary FR (with a white fluorescent light end-of-day treatment) induced approximately 90 per cent. The ecological significance of this difference is discussed with respect to shade detection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00388211
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  • 8
    Electronic Resource
    Electronic Resource
    Rapid photomodulation of stem extension in light-grownSinapis alba L. (1980)
    Springer
    Planta 150 (1980), S. 95-101 
    Details
    ISSN: 1432-2048
    Keywords: Ligth (growth regulation) ; Photomodulation ; Phytochrome ; Sinapis ; Stem growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Treatment of the whole of aSinapis alba plant with supplementary far-red light (FR), in back-ground white light (WL), induces a rapid increase in stem extension rate. This rapid increase is regulated by the light environment of the stem itself. Supplementary FR to the stem increases extension rate after a lag period of 10–15 min. A lag period of 3–4 h follows FR irradiation of the leaf, before an increase in extension rate is detectable. When the stem is given supplementary FR, the change in extension rate which is induced increases with increasing FR fluence rate, and with decreasing phytochrome photoequilibrium. There is no difference between the effects of supplementary FR λmax 719 nm and supplementary FR λmax 739 nm for these relationships. The increase in extension rate induced by supplementary FR is reversed by an increase in the fluence rate of red light (R). These data indicate that the response is controlled by phytochrome photoequilibrium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582351
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  • 9
    Electronic Resource
    Electronic Resource
    A systematic relationship between phytochrome-controlled development and species habitat, for plants grown in simulated natural radiation (1979)
    Springer
    Planta 145 (1979), S. 253-258 
    Details
    ISSN: 1432-2048
    Keywords: Phytochrome ; Development habitat ; Natural radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A survey of the responsiveness of plant species, typical of open and shade habitats, to simulated natural shade-light quality (i.e. white light plus supplementary far-red) has demonstrated a systematic relationship between habitat and certain developmental responses. Supplementary far-red light has a much greater effect on stem extension rate, petiole length, and leaf dry weight: stem dry weight ratio of the open habitat, shade-intolerant species. Far-red effects on leaf chlorophyll content show no such systematic grading. These results are discussed in relation to habitat adaptation. In most cases, the relationship between developmental response and the estimated phytochrome photoequilibrium, which is established by the radiation treatment, is linear. This is taken as an indication of phytochrome involvement in shade perception.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00454449
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  • 10
    Electronic Resource
    Electronic Resource
    Absence of fluence rate dependency of phytochrome modulation of stem extension in light-grown Sinapis alba L. (1981)
    Springer
    Planta 151 (1981), S. 497-498 
    Details
    ISSN: 1432-2048
    Keywords: Cycling rate ; Phytochrome ; Sinapis ; Stem extension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In background white light, supplementary far-red (λmax 700 nm) is an order of magnitude less effective than supplementary far-red (λmax 739 nm) in the stimulation of stem extension in Sinapis alba. The relationship between phytochrome photoequilibrium and extension rate increase for the two supplementary far-red treatments is, however, very similar. This evidence indicates that phytochrome cycling is not involved in the phytochrome control of stem extension in light-grown Sinapis alba and that the response to supplementary far-red light is not fluence rate (irradiance) dependent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00386545
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