22 research outputs found

    True Digital Control of carbon dioxide in agricultural crop growth experiments

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    The paper outlines the design of Proportional-Integral-Plus (PIP) controllers for regulating the level of carbon dioxide in a closed loop apparatus used for carbon-11 tracer experiments in plants. The system, which behaves essentially as an integrator with a four sample time delay, is quite difficult to control using conventional methods because of the rather limited pulse-width-modulated input signal. In contrast, optimal PIP designs, which exploit a special Non-Minimum State Space (NMSS) form within a Linear Quadratic (LQ) optimisation context, are able to maintain the gas concentration to within 2 ppm of the set point

    Phloem Import and Storage Metabolism Are Highly Coordinated by the Low Oxygen Concentrations within Developing Wheat Seeds

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    We studied the influence of the internal oxygen concentration in seeds of wheat (Triticum aestivum) on storage metabolism and its relation to phloem import of nutrients. Wheat seeds that were developing at ambient oxygen (21%) were found to be hypoxic (2.1%). Altering the oxygen supply by decreasing or increasing the external oxygen concentration induced parallel changes in the internal oxygen tension. However, the decrease in internal concentration was proportionally less than the reduction in external oxygen. This indicates that decreasing the oxygen supply induces short-term adaptive responses to reduce oxygen consumption of the seeds. When external oxygen was decreased to 8%, internal oxygen decreased to approximately 0.5% leading to a decrease in energy production via respiration. Conversely, increasing the external oxygen concentration above ambient levels increased the oxygen content as well as the energy status of the seeds, indicating that under normal conditions the oxygen supply is strongly limiting for energy metabolism in developing wheat seeds. The intermediate metabolites of seed storage metabolism were not substantially affected when oxygen was either increased or decreased. However, at subambient external oxygen concentrations (8%) the metabolic flux of carbon into starch and protein, measured by injecting (14)C-Suc into the seeds, was reduced by 17% and 32%, respectively, whereas no significant effect was observed at superambient (40%) oxygen. The observed decrease in biosynthetic fluxes to storage compounds is suggested to be part of an adaptive response to reduce energy consumption preventing excessive oxygen consumption when oxygen supply is limited. Phloem transport toward ears exposed to low (8%) oxygen was significantly reduced within 1 h, whereas exposing ears to elevated oxygen (40%) had no significant effect. This contrasts with the situation where the distribution of assimilates has been modified by removing the lower source leaves from the plant, resulting in less assimilates transported to the ear in favor of transport to the lower parts of the plant. Under these conditions, with two strongly competing sinks, elevated oxygen (40%) did lead to a strong increase in phloem transport to the ear. The results show that sink metabolism is affected by the prevailing low oxygen concentrations in developing wheat seeds, determining the import rate of assimilates via the phloem

    LWS observations of the bright rimmed globule IC1396N

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    We present the first far-infrared spectrum of the IRAS source associated with IC 1396N, located in the HII region IC 1396 together with submillimeter and millimeter photometry. A rich spectrum of CO, OH, and H_2_O lines are detected in the ISO-LWS spectrum, indicative of a warm, dense region, probably shock excited, around the source. Among the fine structure lines, [OIII] and [NIII] are also detected and can be explained by the presence of the O6 star HD206267 approximately 16pc away. The far infrared and submillimeter spectral energy distribution is fitted with a model assuming spherical grey-bodies with a radial power law of density and temperature. An accurate measure of the bolometric luminosity and an estimate of the total envelope mass are obtained
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