Light recommendations for horticultural crops often focus on the optimal daily light integral (DLI) without regard to how that light is delivered throughout each day. Because photosynthesis is more efficient at lower photosynthetic photon flux density (PPFD), we hypothesized that longer photoperiods with lower PPFD results in faster growth than shorter photoperiods with higher PPFD and the same DLI. We quantified the effect of different photoperiods, all providing the same DLI, on photosynthesis and growth of two leafy greens. Mizuna (Brassica rapa var. japonica) and lettuce (Lactuca sativa) “Little Gem” were grown from seed in a controlled environment chamber (20 °C and 819 µmol·mol−1 CO2) under six photoperiods (10, 12, 14, 16, 18, and 20 h). LED fixtures provided white light and PPFD was adjusted so each treatment received a DLI of 16 mol·m−2·d−1. Mizuna and lettuce were harvested 30 and 41 days after planting, respectively. Longer photoperiods with lower PPFD increased light interception, chlorophyll content index, quantum yield of photosystem II, and aboveground biomass, but decreased instantaneous CO2 assimilation of lettuce and mizuna. Aboveground biomass increased 16.0% in lettuce and 18.7% in mizuna in response to increasing the photoperiod from 10 to 20 h. In summary, extending the photoperiod and lowering PPFD increases growth of lettuce and mizuna by increasing light interception and the quantum yield of photosystem II.
In this paper we report on the radiation stability of silicon carbide and diamond membranes as potential x-ray lithography mask carriers. Silicon carbide membranes have been produced by epitaxial chemical vapor deposition (CVD). Diamond membranes have been produced in tension with diameters up to 2.5 cm using a microwave plasma CVD process. The stability of these membranes upon exposure to x rays has been studied. The materials were characterized before and after irradiation for their stress, Young’s modulus, infrared absorption from 2.5 to 25 μm, and visible transmission from 300 to 800 nm. The x-ray exposures were performed using the Center for X-ray Lithography beamlines at the Aladdin synchrotron at the University of Wisconsin. These beamlines provide a broadband x-ray spectrum from 900 to 5000 eV. Incident doses of 6700 and 2400 J/cm2 were delivered to the silicon carbide and diamond samples, respectively. Both materials were found to be stable for these exposure levels within the accuracy of the experimental methods.
A small clinical survey was undertaken at East Carolina University School of Medicine to examine the factors which influenced the decisions of five families to continue pregnancies after a chromosomal abnormality was detected. Little has been published concerning the psychosocial effects after continuing pregnancies in which the fetus was diagnosed with a chromosome abnormality by amniocentesis. In order to identify the factors that influenced their decisions, an interview with each couple was undertaken using a 25-part questionnaire. This paper addresses the method of interviewing, case material, and background concerning each couple and the summary of the results.
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