Appropriate controls in outdoor UV‐B supplementation experiments
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Abstract Quercus robur L. saplings were exposed in an outdoor experiment to supplemental levels of UV‐8 (280–315 nm) radiation using treatment arrays of cellulose diacetate‐filtered fluorescent lamps that also produce UV‐A (315–400 nm) radiation. Saplings were also exposed to UV‐A radiation alone using control arrays of the same lamps filtered with polyester and to ambient levels of radiation, using arrays of unenergized lamps. The UV‐B treatment was modulated to maintain a 30% elevation above the ambient level of UV‐B radiation, measured by a broad‐band sensor weighted with an erythemal action spectrum. Saplings exposed to UV‐B radiation beneath treatment arrays developed thicker leaves than those beneath ambient and control arrays. Despite the fact that supplemental levels of UV‐A radiation were only a small percentage of ambient levels, apparent UV‐A effects were also recorded. Significant increases in sapling height, lammas shoot length and herbivory by chewing insects were observed under treatment and control arrays, relative to ambient, but there were no differences between the responses of saplings under treatment and control. These data imply that supplemental UV‐A radiation or other effects associated with energised lamps can significantly affect plant growth parameters and herbivory in outdoor studies. We conclude that the results from current outdoor UV‐B supplementation experiments that lack control exposures using polyester‐filtered lamps need to be interpreted with caution and that future supplementation experiments should include appropriate controls.Cite
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Porous SiC Ceramics with Multiple Pore Structure Fabricated via Gelcasting and Solid State Sintering
Porous SiC ceramics with multiple pore structures were fabricated via gelcasting and solid state sintering.A novel gelling agent of Isobam was applied and PMMA was used as both foam stabilizer and pore forming agent.The mechanical properties of porous SiC ceramics were investigated as functions of PMMA content, rotating speed of ball mill, and sintering temperature.With PMMA content increasing from 5wt% to 20wt%, the foaming effect was inhibited while the stability of bubbles increased.When the rotating speed was 220 r/min, the open porosities of the as-prepared SiC ceramics sintered at 2100 varied ℃ from 51.5% to 72.8%, and compressive strength varied from 7.9 to 48.2 MPa.With the rotating speed increasing from 220 to 280 r/min, the foaming effect was aggravated and the porosities of SiC ceramics sintered at 2100 increased.℃ While the sintering temperature increasing from 2050 to 2150 , ℃ the SiC ceramics prepared with PMMA content of 20wt% at rotating speed of 220 r/min decreased in the open porosities while increased in compressive strength.
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ZrB2 based composites containing 10 vol.-% carbon nanotubes (CNTs) are synthesised by spark plasma sintering at temperatures ranging from 1600 to 18008C and at an applied pressure of 25 MPa. The effects of sintering temperature on densification behaviour, microstructural evolutions and mechanical properties are presented. Results indicate that ZrB2-CNT composites fabricated at 16508C have the optimal combination of dense microstructure and properties. The fracture toughness is sensitive to the temperature change and reaches 7.2 MPa m1/2 for the CNT toughened ZrB2 ceramics, which is higher than the measured result for monolithic ZrB2 (3.3 MPa m1/2). The crack deflection and CNT pullout are the dominant toughening mechanisms.
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Long-term decreases in summertime ozone over Lauder, New Zealand (45 degrees S), are shown to have led to substantial increases in peak ultraviolet (UV) radiation intensities. In the summer of 1998-99, the peak sunburning UV radiation was about 12 percent more than in the first years of the decade. Larger increases were seen for DNA-damaging UV radiation and plant-damaging UV radiation, whereas UV-A (315 to 400 nanometers) radiation, which is insensitive to ozone, showed no increase, in agreement with model calculations. These results provide strong evidence of human-induced increases in UV radiation, in a region where baseline levels of UV radiation were already relatively high.
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